Remove_namespaces! for Nokogiri XML document parsing

I've come upon a situation where incoming XML is namespaced, e.g.

```xml
<songs xmlns="disasterous">
  <song title="Never Gonna Give You Up"/>
</songs>
```

Consuming such XML fails because accessing elements in representable doesn't take namespaced tags into account. I've found a quick and dirty solution, using (remove_namespaces!)[http://nokogiri.org/Nokogiri/XML/Document.html#method-i-remove_namespaces-21]. You can find the solution and the accompanying test in pull request.

That said, I am not really sure this is the best way to go. Maybe representable could use namespaced access, as explained (here)[http://stackoverflow.com/questions/1737572/why-doesnt-nokogiri-xpath-like-xmlns-declarations], but not sure how to apply it. Also, this (article)[http://tenderlovemaking.com/2009/04/23/namespaces-in-xml.html], referenced from Nokogiri docs, really gives some thought. 

But maybe none of this apply to consuming XML in representers. What do you think?